Preslia 82: 81–96, 2010
81
Naturalized plants have smaller genomes than their non-invading
relatives: a flow cytometric analysis of the Czech alien flora
Naturalizované rostliny mají menší genom než neinvadující druhy: cytometrická analýza nepůvodních
druhů české květeny
Magdalena K u b e š o v á1,2, Lenka M o r a v c o v á1, Jan S u d a2,1, Vojtěch J a r o š í k3,1 &
Petr P y š e k1,3
1
Institute of Botany, Academy of Sciences of the Czech Republic, CZ-252 43 Průhonice,
Czech Republic, e-mail: [email protected], [email protected], [email protected];
2
Department of Botany, Faculty of Science, Charles University in Prague, Benátská 2, CZ128 01 Prague, Czech Republic, e-mail: [email protected]; 3Department of Ecology,
Faculty of Science, Charles University in Prague, Viničná 7, CZ-128 44 Prague, Czech
Republic, e-mail: [email protected]
Kubešová M., Moravcová L., Suda J., Jarošík V. & Pyšek P. (2010): Naturalized plants have smaller
genomes than their non-invading relatives: a flow cytometric analysis of the Czech alien flora. –
Preslia 82: 81–96.
Genome size has been suggested as one of the traits associated with invasiveness of plant species. To
provide a quantitative insight into the role of this trait, we estimated nuclear DNA content in 93 alien
species naturalized in the Czech Republic, belonging to 32 families, by using flow cytometry, and
compared it with the values reported for non-invading congeneric and confamilial species from the
Plant DNA C-values database. Species naturalized in the Czech Republic have significantly smaller
genomes than their congeners not known to be naturalized or invasive in any part of the world. This
trend is supported at the family level: alien species naturalized in the Czech flora have on average
a smaller genome than is the mean value for non-invading confamilials. Moreover, naturalized and
non-invading species clearly differed in the frequency of five genome size categories; this difference
was mainly due to very small genomes prevailing and intermediate to very large genomes underrepresented in the former group. Our results provide the first quantitative support for association of
genome size with invasiveness, based on a large set of alien species across a number of plant families. However, there was no difference in the genome size of invasive species compared to naturalized but non-invasive. This suggests that small genome size provides alien plants with an advantage
already at the stage of naturalization and need not be necessarily associated with the final stage of
the process, i.e. invasion.
K e y w o r d s: alien plants, confamilials, congeners, C-value, flow cytometry, genome size, invasive species, large genome constraint hypothesis, nuclear DNA content, plant invasions
Introduction
The numbers of invasive species in various parts of the world continue to increase, representing a serious threat to biodiversity worldwide (e.g. Meyerson & Mooney 2007,
Blackburn et al. 2009, Hulme et al. 2009b, McGeoch et al. 2010). As a result, biological
invasions have been receiving serious attention from both scientists and practitioners and
research in invasive plant and animal species has been increasing exponentially (e.g. Crall
et al. 2006, Pyšek et al. 2006, 2008, Lambdon et al. 2008, Ricciardi & MacIsaac 2008,
Chytrý et al. 2009, DAISIE 2009, Davis 2009). The knowledge of ecological impacts on
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native biodiversity and ecosystem functioning improved dramatically in the last decade
(e.g. Levine et al. 2003, Gaertner et al. 2009, Hejda et al. 2009a, Nentwig et al. 2010, Vilà
et al. 2010), and it is now widely recognized that invasive species incur serious economic
costs (Binimelis et al. 2007, Kettunen et al. 2009, Vilà et al. 2010). The awareness of the
magnitude of problem is stimulating not only management efforts (Keller et al. 2007,
Richardson et al. 2007, Hulme et al. 2008, 2009a, Simberloff 2009, McGeoch et al. 2010),
but also research aimed at deeper understanding of underlying processes and determinants
of naturalization and invasiveness (e.g. Pyšek et al. 2008, 2009a, Blackburn et al. 2009,
Davis 2009, Essl et al. 2009, Štajerová et al. 2009). Within this research realm, an effort to
identify biological and ecological traits conferring invasiveness is as well established as
the field of invasion biology itself (see Pyšek & Richardson 2007 for a review). Recent
developments, including the development of new technologies (Richardson & Pyšek
2008), in particular molecular techniques, now make it possible to include traits that were
until not long ago impossible to consider in multispecies studies focusing on determinants
of invasiveness (Pyšek & Richardson 2007). The amount of nuclear DNA (genome size) is
one of the traits for which knowledge has improved dramatically in the last decade, largely
due to the advent and spread of flow cytometry (Kron et al. 2007, Ekrt et al. 2009).
Genome size is a fundamental biological parameter involved in the scaling of both
plants and animals (Gregory 2005). DNA is known to play not only a qualitative (i.e.
genic) role but also a quantitative one because of its direct and sequence-independent
influence on cellular (and by extension, organismal) characteristics. Correlations between
genome size and plant traits are many and range from nuclear and cell volumes through the
duration of cell cycle (both meiotic and mitotic) up to seed size and specific leaf area
(reviewed by Leitch & Bennett 2007, see also Loureiro et al. 2010). Through concomitant
changes in cellular parameters, genome size affects several aspects of a plant’s development. Minimum generation time (i.e. time to flowering) and life history (i.e. whether
ephemeral, annual or perennial) are illustrative examples of developmental traits constrained by the amount of nuclear DNA. On average, ephemerals (plants completing their
life cycle in less then seven weeks) have been shown to possess the smallest genomes, followed by annuals, whereas obligate herbaceous perennials have the highest DNA amounts
(Bennett 1972). Whereas species with small genomes can display any developmental life
history, their large-genome counterparts are restricted to an obligate perennial life history.
Large genomes also impose constraints on ecological behaviour, influencing where a plant
may grow and its chances of survival in a changing world (Knight et al. 2005, Vidic et al.
2009). In addition, traits associated with genome size (seed size and mass, and the rate of
developmental processes in particular) may co-determine the life strategy adopted by the
plant (i.e. whether competitor, stress tolerator or ruderal). In their study on 156 weedy
angiosperm species, Bennett et al. (1998) showed that the probability of being recognized
as a weed decreases with increasing genome size.
On the same conceptual basis, small genomes have been suggested as a prerequisite for
plant invasiveness because species with low nuclear DNA content usually produce many
light seeds and their establishment is fast (Rejmánek 1996). In addition, invasions typically occur in disturbed habitats (Davis et al. 2000, Chytrý et al. 2005, 2008) and small
genomes have been shown to represent an evolutionary advantage in time-limited environments (Bennett 1987). In his “theory of seed plant invasiveness”, Rejmánek listed a low
amount of nuclear DNA among the most important factors contributing to the invasiveness
Kubešová et al.: Naturalized plants have small genomes
83
of seed plants (Rejmánek 1996, 2000, Rejmánek et al. 2005). Experimental support for
this conclusion comes mainly from comprehensive studies on genome size variation in the
genus Pinus (Wakamiya et al. 1993, Grotkopp et al. 2002, 2004). Invasiveness of pines,
particularly of wind-dispersed species, was shown to be negatively associated with both
genome size and seed mass (Grotkopp et al. 2002). Smaller genomes in invasive species as
compared to their non-invasive congeners have also been found in some other genera such
as Senecio (Lawrence 1985) or Acacia (Mukherjee & Sharma 1990), although the number
of analyzed invasive species was usually quite low. In addition, a negative relationship was
observed between the genome size of three Briza species and the invaded area (Rejmánek
1996).
Despite the pieces of evidence mentioned above for the role of genome size in plant
invasions, a systematic study aimed at comparing genome sizes in invasive plant species
and their non-invasive counterparts across different taxonomic groups is still lacking. To
fill this gap, we determined nuclear DNA amounts in a representative set of alien species
occurring in the Czech Republic and compared their genome size values with those of
non-invasive congeners and confamilials. Specifically, we addressed the following questions: (i) What is the distribution of holoploid genome sizes in alien species and how it differs from the general pattern found in angiosperms? (ii) Which factors affect the genome
size of alien species? Is genome size related to the invasion status? (iii) Do alien species
differ in genome size from their non-invasive congeners and confamilials?
Material and methods
Analyzed species
The species set included 93 neophytes (alien species introduced after 1500 A.D.; see
Pyšek et al. 2002, 2004) occurring in the flora of the Czech Republic. They belonged to 70
genera and 32 families according to the Angiosperm phylogeny group classification
(Stevens 2001). Seeds were collected in the field during 2005–2007 (see Electronic
Appendix 1). Seedlings were germinated in a growth chamber and cultivated in the experimental garden of the Institute of Botany, Academy of Sciences, Průhonice, Czech Republic (49°59'30''N, 14°34'00''E, ca 320 m a.s.l.). Fresh young leaf tissue was used for genome
size estimation. Herbarium vouchers are kept at PRA.
Species’ invasion status in the Czech Republic (casual; naturalized; invasive) was taken
from Pyšek et al. (2002). The vast majority of species were naturalized, only three (Ambrosia trifida, Bidens connata and Panicum miliaceum) were casual; for the sake of simplicity,
all the species analyzed are further referred to as ‘naturalized’. Of these naturalized species, 41 were invasive and 49 naturalized but not invasive (sensu Richardson et al. 2000,
Pyšek et al. 2004). Each species was further characterized (see Table 1) by its life history
(annual; monocarpic perennial; polycarpic perennial) and moisture score. The moisture
score was calculated by using data from Hejda et al. (2009b); this paper and associated
database give, for species alien to the Czech Republic, information on habitats in which
they occur in their native range. These habitats were classified using a 5-degree ordinal
scale (1-dry, 3-mesic, 5-humid, with 2 and 4 representing transitions) and average value
was used as the moisture score. Of our species set, habitat data for 58 species were available in Hejda et al. (2009b); for remaining species we used the average Ellenberg’s indicator
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Preslia 82: 81–96, 2010
value for moisture (Ellenberg et al. 1992), transformed to a 5-degree scale as follows:
1–3=1, 4=2, 5=3, 6–7=4, 7–9=5.
Genome size estimation
Holoploid genome sizes (C-values sensu Greilhuber et al. 2005) were determined using
propidium iodide flow cytometry following the simplified two-step protocol as described
by Doležel et al. (2007). Briefly, young intact leaf tissue of the analyzed plant was
chopped together with an appropriate internal reference standard in 0.5 ml of ice-cold Otto
I buffer (0.1 M citric acid, 0.5% Tween 20; Otto 1990). The sample was filtered through
42-μm nylon mesh, and incubated 10 min at room temperature. The staining solution consisted of 1 ml of Otto II buffer (0.4 M Na2HPO4 · 12H2O) supplemented with propidium
iodide and RNase IIA (both at final concentrations of 50 μg/ml) and β-mercaptoethanol
(2 μl/ml). The fluorescence intensity of isolated nuclei (5000 particles) was recorded using
Partec CyFlow SL cytometer equipped with a diode-pumped solid state laser 532 nm
(Cobolt Samba, 100 mW output power). Each sample was analyzed at least three times on
different days; only analyses with a between-day fluctuation below 3% were considered.
The following species were used as internal reference standards (Doležel et al. 2007):
Solanum lycopersicum 'Stupické polní rané' (2C = 1.90 pg), Glycine max 'Polanka' (2C =
2.30 pg), Bellis perennis (2C = 3.46 pg), Zea mays 'CE-777' (2C = 5.47 pg), Pisum sativum
'Ctirad' (2C = 8.76 pg) and Vicia faba 'Inovec' (2C = 26.92 pg). Pisum sativum 'Ctirad'
(Doležel et al. 1998) served as a primary reference standard, with 2C-value of 8.76 pg as
recommended by Greilhuber et al. (2007). Genome sizes of other reference species were
calibrated against Pisum, based on three measurements on different days. For each analyzed plant, internal standard was selected so that its genome size was close to but not
overlapping with that of the analyzed sample.
Ploidy levels of analyzed naturalized plants were inferred from chromosome numbers
taken from various karyological databases and flora handbooks, including Goldblatt &
Johnson (1979), Marhold et al. (2007), Flora of the Czech Republic (Hejný & Slavík
1988–1992, Slavík 1995–2000, Slavík & Štěpánková 2004), the database of the flora of
the Czech Republic (CzechFlor) and the internal karyological database of plants of the
Czech Republic (both held at the Institute of Botany AS CR, Průhonice). Monoploid
genome sizes (1Cx-values) were calculated as 2C-values / ploidy level.
Reference genome size data
To compare the genome size of naturalized alien plants in the Czech flora with non-invasive species, 2C-values and ploidy levels for plants from corresponding genera and families that are not reported to be naturalized or invasive were extracted from the Plant DNA
C-values database (Bennett & Leitch 2005). Species in this reference data set are referred
to as ‘non-invading’ to reflect not only that they are not invasive (in the sense of Richardson et al. 2000) but neither naturalized, i.e. they do not successfully enter the invasion process. The selection of non-invading congeners and confamilials was made by omitting
from the Plant DNA C-values database any species reported as naturalized or invasive in
any part of the world, based on the updated database of Weber (2003) and other sources. In
some cases, the ploidy level taken from the Plant DNA C-values database was corrected so
that the basic chromosome number (x) was the same for both naturalized species and their
Kubešová et al.: Naturalized plants have small genomes
85
non-invading congeners. Reference genome size data were available for 45 congeneric
and 31 confamilial non-invading counterparts.
Statistical analysis
Comparison of genome size categories between naturalized plants of the Czech flora and
non-invading species taken from the Plant DNA C-values database was done by G-test on
a contingency table (e.g. Crawley 2002, p. 548–550).
The effect of invasion status (41 invasive vs 51 non-invasive species, the latter including 48 naturalized and three casual; Oxybaphus nyctagineus was excluded because of nonavailable moisture data), life history and moisture score on 2C-values was analyzed by
general linear model. The most parsimonious model was selected by a stepwise procedure,
beginning with the maximal model (containing all predictors and all their possible interactions) and proceeding by the elimination of non-significant terms, using deletion tests.
This was done by an automatic step-wise process of model simplification of deviance
tables, based on Akaike Information Criterion (AIC) (program Spotfire S-Plus v. 8.1,
TIBCO Software Inc. 2008; e.g. Crawley 2002). Observed power of the chosen model
(e.g. Steidel & Thomas 2001) was computed for α = 0.05 in SPSS v. 18 (SPSS Inc. 2010).
Paired t-tests (Sokal & Rohlf 1995) were used for comparisons of 2C- and Cx-values of
naturalized aliens with corresponding mean values of their non-invading congeners, and
of mean 2C-values of naturalized aliens with corresponding mean values of their noninvading confamilials. All 2C-values were ln-transformed to normalize the data, and then
checked for homogeneity of variance. The general linear model was checked by plotting
standardized residuals against fitted values, and by normal probability plots (Crawley
1993).
Results
Genome size variation in naturalized alien species
Flow cytometric analyses yielded histograms with mean coefficients of variation (CVs) of
3.18% and 2.50% for the sample and internal reference standard, respectively (Fig. 1).
Genome size values were determined in one APG family (Phrymaceae) and 66 species
for the first time (Table 1). 1C-values of analyzed plants varied from 0.24 pg in
Sisymbrium loeselii to 15.27 pg in Rudbeckia laciniata, spanning ~64-fold range. The
majority of naturalized species possessed low nuclear DNA amounts, with mean 1C-value
of 1.93 pg and median of 1.17 pg. The distribution of genome sizes was highly skewed
(Fig. 2). The most common were plants with 1C-values between 0.4 and 0.6 pg; other
classes were much less frequent, and only four species had 1C-values above 4.4 pg. The
same pattern was obtained when the species analyzed were attributed to five genome size
categories as defined by Leitch et al. (1998). Very small genomes (1C ≤ 1.4 pg) were represented by 49 species, small genomes (1.4 pg < 1C ≤ 3.5 pg) by 36 species, intermediate
genomes (3.5 pg < 1C ≤ 14.0 pg) by seven species, and large genomes (14.0 pg < 1C ≤ 35.0
pg) by one species. Plants with very large genomes (1C > 35 pg) were not present in our
species set. Compared to non-invading species (Table 2), naturalized species had more
86
Preslia 82: 81–96, 2010
200
80
Solanum
Sisymbrium (G1)
Number of nuclei
120
Sisymbrium (G2)
A
160
40
0
0
200
400
600
800
1000
Relative fluorescence
300
B
180
Vicia
Helianthus
Number of nuclei
240
120
60
0
0
200
400
600
800
1000
Relative fluorescence
Fig. 1. – Flow cytometric histograms showing genome size determination in species with very small (Sisymbrium
altissimum, 2C = 0.52 pg; panel A) and large (Helianthus tuberosus, 2C = 23.89 pg; panel B) genomes. Nuclei of
both the analyzed sample and internal reference standard were isolated, stained with propidium iodide and analyzed simultaneously. Solanum lycopersicum and Vicia faba, respectively, were used as reference standards.
often very small and small genomes, and less often intermediate to very large genomes
than expected by chance (G-test on contingency table: χ2 = 61.15, df = 2, P < 0.0001).
Ploidy levels in the species set analyzed varied from diploid to dodecaploid (Table 1),
and monoploid genome sizes (1Cx-values) ranged from 0.12 pg in 8x Juncus tenuis to
4.38 in 2x Virga strigosa (= 38-fold range).
Factors affecting genome size of naturalized alien species
None of the examined explanatory variables (invasion status, life history, moisture score)
had a significant effect on genome size (full model: F = 1.141; df = 11, 80; NS; observed
power = 0.486).
87
Kubešová et al.: Naturalized plants have small genomes
18
Number of species
15
12
9
6
3
0
0
2
4
6
8
10
12
14
16
1C-value (pg DNA)
Fig. 2. – Distribution of 1C-values (pg means) in 93 naturalized alien species occurring in the Czech Republic.
Table 2. – Contingency table on observed and expected counts of genome size categories according to Leitch et al.
(1998) in naturalized plants of the Czech flora (n = 93) and non-invading species (n = 4148) taken from the Plant
DNA C-values database (Bennett & Leitch 2005). Genome size categories “intermediate”, “large” and “very
large” were pooled together due to small sample sizes in these categories for naturalized species. Statistics are
given in the text.
Genome size category
Very small (1C ≤ 1.40 pg)
Small (1C = 1.41–3.50 pg)
Intermediate to very large (1C ≥ 3.51 pg)
Naturalized species
Non-invading species
observed
expected
observed
expected
49
36
8
30.0
22.1
40.9
1287
958
1903
1306.7
972.2
1869.1
Genome size in naturalized alien species vs their non-invading relatives
Naturalized aliens had significantly smaller holoploid and monoploid genome sizes than
their non-invading congeners (two-sided paired t-tests: 2C-values t = 2.161, df = 45, P =
0.04; Cx-values t = 2.70, df = 44, P = 0.01), and the same held for 2C-values on
confamilials (t = 3.161, df = 30, P = 0.004). Visual inspection of data indicates that naturalized aliens had smaller genomes in 19 of 31 families considered (Fig. 3).
88
Preslia 82: 81–96, 2010
Table 1. – List of analyzed species, with their family affiliation, life history, LH (an – annual; mono – monocarpic
perennial; per – polycarpic perennial), invasion status, moisture score (see Methods for calculation) and genome
size characteristics: mean holoploid genome sizes (2C-values with standard deviation, and 1C-values in
picograms of DNA and megabase pairs; 1 pg = 978 Mbp), ploidy levels, monoploid genome sizes (1Cx-values),
and internal reference standard used (B – Bellis perennis; G – Glycine max; P – Pisum sativum; S – Solanum
lycopersicum; V – Vicia faba; Z – Zea mays). Invasion status was taken from Pyšek et al. (2002); species marked
with asterisk are classified differently to better reflect situation in sampled localities. Species analyzed for the
first time are shown in bold; those used for comparison with non-invading congeners are designated by “+” after
species name. Empty cells – data not available.
Species
Family
Life
Invasion
history status
Moisture 2C-value S.D. 1C-value 1C-value Ploidy
(pg DNA) (Mbp)
score (pg DNA)
level
1Cx- Internal
value standard
(pg DNA)
Abutilon theophrasti
Malvaceae
Amaranthus albus +
Amaranthaceae
Amaranthus blitoides + Amaranthaceae
Amaranthus powellii +
Amaranthaceae
Amaranthus retroflexus + Amaranthaceae
Ambrosia artemisiifolia Asteraceae
Ambrosia trifida
Asteraceae
Angelica archangelica Apiaceae
Antirrhinum majus
Plantaginaceae
Arabis alpina
Brassicaceae
Asclepias syriaca
Apocynaceae
Aster lanceolatus +
Asteraceae
Bidens connata
Asteraceae
Bidens frondosa
Asteraceae
Bunias orientalis +
Brassicaceae
Cannabis ruderalis +
Cannabaceae
Cardamine chelidonia + Brassicaceae
Claytonia alsinoides
Portulacaceae
Collomia grandiflora
Polemoniaceae
Consolida orientalis
Ranunculaceae
Conyza canadensis
Asteraceae
Corydalis lutea
Papaveraceae
Cuscuta campestris
Convolvulaceae
Datura stramonium +
Solanaceae
Digitalis purpurea
Plantaginaceae
Duchesnea indica
Rosaceae
Echinocystis lobata
Cucurbitaceae
Echinops sphaerocephalus Asteraceae
Epilobium ciliatum +
Onagraceae
Epilobium dodonaei + Onagraceae
Erigeron annuus
Asteraceae
Erucastrum gallicum
Brassicaceae
Galega officinalis
Fabaceae
Galinsoga parviflora
Asteraceae
Galinsoga quadriradiata Asteraceae
Geranium pyrenaicum Geraniaceae
Helianthus tuberosus + Asteraceae
Heracleum
mantegazzianum +
Apiaceae
Hesperis matronalis
Brassicaceae
Hordeum jubatum +
Poaceae
Chenopodium pumilio + Amaranthaceae
Chenopodium strictum + Amaranthaceae
an
an
an
an
an
an
an
mono
mono
per
per
per
an
an
mono
an
mono
an
an
an
an
per
an
an
mono
per
an
per
per
per
mono
mono
per
an
an
per
per
naturalized*
naturalized
naturalized
invasive
invasive
invasive
casual
invasive
naturalized
naturalized
naturalized
invasive
casual
invasive
invasive
naturalized*
naturalized
naturalized
naturalized
naturalized
invasive
naturalized
invasive
naturalized
invasive
naturalized
invasive
invasive
invasive
naturalized
invasive
naturalized
naturalized
invasive
invasive
invasive
invasive
4.0
2.0
2.3
4.0
2.2
3.0
3.7
5.0
1.0
2.0
3.0
4.0
5.0
5.0
2.1
2.5
3.0
4.0
3.0
2.4
1.8
1.0
3.0
2.0
2.4
3.0
3.0
2.5
4.0
5.0
2.0
2.0
3.0
3.0
2.0
3.0
4.0
2.17
1.11
1.13
1.02
1.12
2.32
3.82
6.46
1.17
0.83
0.84
5.41
6.44
3.20
5.40
1.81
0.71
6.91
4.15
4.57
0.91
1.26
0.96
4.19
1.86
3.45
1.49
8.02
0.82
1.17
4.33
2.08
4.42
1.47
4.03
2.87
23.89
0.02
0.00
0.00
0.00
0.01
0.03
0.03
0.10
0.01
0.02
0.03
0.01
0.06
0.02
0.02
0.01
0.00
0.05
0.04
0.04
0.01
0.01
0.00
0.05
0.01
0.01
0.01
0.11
0.03
0.01
0.05
0.01
0.04
0.01
0.04
0.02
0.09
1.09
0.55
0.56
0.51
0.56
1.16
1.91
3.23
0.58
0.42
0.42
2.71
3.22
1.60
2.70
0.91
0.36
3.45
2.08
2.28
0.45
0.63
0.48
2.09
0.93
1.72
0.74
4.01
0.41
0.59
2.17
1.04
2.21
0.74
2.02
1.44
11.95
1061.1
540.8
552.1
496.8
546.2
1134.5
1865.5
3158.0
570.7
406.8
409.8
2647.0
3150.6
1566.3
2641.6
885.1
349.1
3377.0
2030.3
2233.3
443.5
616.1
469.4
2047.4
910.0
1686.6
727.6
3923.7
401.0
573.1
2118.8
1018.6
2161.4
720.3
1972.6
1403.9
11682.7
6
4
4
4
4
4
2
2
2
2
2
8
4
4
2
2
4
0.36
0.28
0.28
0.25
0.28
0.58
1.91
3.23
0.58
0.42
0.42
0.68
1.61
0.80
2.70
0.91
0.18
2
2
2
4
8
2
8
12
4
4
4
4
3
4
2
4
2
2
12
2.08
2.28
0.45
0.32
0.12
2.09
0.23
0.29
0.37
2.01
0.21
0.29
1.44
0.52
2.21
1.01
0.74
1.44
1.99
B
S
G
B
S
B
P
P
S
S
S
P
Z
P
P
S
S
P
B
P
S
S
S
Z
G
P
S
Z
S
S
Z
B
G
S
Z
G
V
mono
per
an
an
an
invasive
naturalized
naturalized
naturalized
naturalized
3.0
3.4
2.0
1.0
3.1
3.56
7.61
17.38
0.73
1.60
0.03
0.07
0.09
0.02
0.01
1.78
3.80
8.69
0.37
0.80
1740.8
3719.3
8499.8
357.0
782.4
2
4
4
2
4
1.78
1.90
4.35
0.37
0.40
Z
P
P
P
P
89
Kubešová et al.: Naturalized plants have small genomes
Species
Family
Life
Invasion
history status
Moisture 2C-value S.D. 1C-value 1C-value Ploidy
(pg DNA) (Mbp)
score (pg DNA)
level
1Cx- Internal
value standard
(pg DNA)
Impatiens glandulifera + Balsaminaceae
Impatiens parviflora + Balsaminaceae
Imperatoria ostruthium Apiaceae
Inula helenium +
Asteraceae
Iva xanthiifolia
Asteraceae
Juncus tenuis +
Juncaceae
Kochia scoparia
Amaranthaceae
Lepidium densiflorum + Brassicaceae
Lupinus polyphyllus + Fabaceae
Lychnis coronaria
Caryophyllaceae
Lysimachia punctata
Primulaceae
Matricaria discoidea + Asteraceae
Medicago sativa +
Fabaceae
Mimulus guttatus
Phrymaceae
Myrrhis odorata
Apiaceae
Oenothera biennis +
Onagraceae
Oenothera glazoviana + Onagraceae
Oxalis corniculata
subsp. repens +
Oxalidaceae
Oxalis dillenii +
Oxalidaceae
Oxalis fontana +
Oxalidaceae
Oxybaphus nyctagineus Nyctaginaceae
Panicum capillare +
Poaceae
Panicum miliaceum +
Poaceae
Phytolacca esculenta + Phytolaccaceae
Potentila intermedia + Rosaceae
Rudbeckia hirta
Asteraceae
Rudbeckia laciniata
Asteraceae
Rumex alpinus +
Polygonaceae
Rumex longifolius +
Polygonaceae
Rumex patientia +
Polygonaceae
Rumex thyrsiflorus +
Polygonaceae
Scutellaria altissima
Lamiaceae
Sedum hispanicum
Crassulaceae
Sedum rupestre
Crassulaceae
Sedum spurium +
Crassulaceae
Senecio inaequidens + Asteraceae
Senecio vernalis +
Asteraceae
Setaria faberi +
Poaceae
Silene dichotoma +
Caryophyllaceae
Sisymbrium altissimum Brassicaceae
Sisymbrium loeselii
Brassicaceae
Sisymbrium strictissimum Brassicaceae
Smyrnium perfoliatum Apiaceae
Solidago canadensis
Asteraceae
Solidago gigantea
Asteraceae
Telekia speciosa
Asteraceae
Trifolium hybridum +
Fabaceae
Veronica persica +
Plantaginaceae
Vicia grandiflora +
Fabaceae
Virga strigosa
Dipsacaceae
Xanthium albinum
Asteraceae
an
an
per
mono
an
per
an
mono
per
mono
per
an
per
per
per
mono
mono
invasive
invasive
invasive
naturalized
naturalized
invasive
invasive
naturalized
invasive
naturalized
naturalized
invasive
naturalized*
invasive
invasive
invasive
naturalized
3.3
3.0
3.0
3.0
2.0
3.0
2.3
2.0
3.0
2.0
5.0
3.0
3.0
5.0
5.0
2.0
3.0
1.90
4.26
3.89
4.53
6.34
0.92
2.23
0.66
1.60
6.30
4.43
4.70
3.49
0.73
1.81
2.30
2.30
0.01
0.04
0.08
0.01
0.07
0.01
0.01
0.03
0.02
0.17
0.02
0.01
0.03
0.03
0.01
0.02
0.01
0.95
2.13
1.95
2.26
3.17
0.46
1.12
0.33
0.80
3.15
2.21
2.35
1.74
0.37
0.90
1.15
1.15
927.6
2083.6
1904.2
2214.2
3098.8
450.9
1090.5
322.7
783.4
3078.7
2165.8
2298.3
1706.1
357.0
883.1
1124.7
1122.7
2
2
2
2
4
8
2
4
4
2
2
2
4
4
2
2
2
0.95
2.13
1.95
2.26
1.58
0.12
1.12
0.17
0.40
3.15
2.21
2.35
0.87
0.18
0.90
1.15
1.15
B
Z
P
P
Z
S
G
S
S
Z
P
B
S
S
G
S
S
mono
mono
mono
per
an
an
per
mono
per
per
per
per
per
per
per
per
per
per
per
an
an
mono
an
an
per
mono
per
per
per
mono
an
an
mono
an
naturalized*
naturalized
naturalized
naturalized
naturalized
casual
naturalized
naturalized
naturalized
invasive
invasive
invasive
naturalized
invasive
naturalized
invasive
naturalized
naturalized
naturalized*
naturalized
naturalized
naturalized
naturalized
invasive
naturalized
naturalized
invasive
invasive
invasive
invasive
invasive
naturalized
invasive
naturalized
2.0
2.0
3.0
2.11
1.01
1.22
1.89
0.91
2.09
5.68
1.80
14.33
30.54
0.96
3.99
4.87
7.81
0.79
5.39
5.41
4.16
2.90
2.33
2.56
5.89
0.52
0.48
1.39
5.64
2.04
3.65
2.57
1.09
1.38
6.23
8.76
5.18
0.02
0.01
0.01
0.01
0.01
0.04
0.10
0.01
0.09
0.12
0.01
0.07
0.02
0.05
0.03
0.04
0.09
0.03
0.01
0.01
0.02
0.02
0.00
0.00
0.01
0.05
0.01
0.03
0.01
0.01
0.01
0.07
0.05
0.09
1.05
0.50
0.61
0.95
0.45
1.04
2.84
0.90
7.17
15.27
0.48
2.00
2.43
3.90
0.40
2.70
2.70
2.08
1.45
1.16
1.28
2.94
0.26
0.24
0.70
2.82
1.02
1.82
1.29
0.54
0.69
3.11
4.38
2.59
1031.3
491.9
594.1
924.2
443.5
1020.5
2778.5
880.2
7008.3
14935.5
467.0
1951.6
2380.5
3817.1
386.3
2636.2
2643.0
2034.2
1419.6
1138.4
1253.8
2878.7
255.7
233.3
680.2
2758.0
999.5
1782.9
1258.2
532.0
672.9
3046.0
4283.2
2531.6
8
4
4
6
2
4
8
4
4
8
2
6
6
2
4
0.26
0.25
0.30
0.32
0.45
0.52
0.71
0.45
3.58
3.82
0.48
0.67
0.81
3.90
0.20
4
2
4
2
4
2
2
2
4
2
2
4
2
2
4
2
2
4
1.35
2.08
0.73
1.16
0.64
2.94
0.26
0.24
0.35
2.82
1.02
0.91
1.29
0.54
0.34
3.11
4.38
1.29
S
G
G
B
B
B
P
S
P
P
S
B
Z
P
S
S
P
P
B
B
B
P
S
S
S
P
G
Z
S
S
S
P
Z
P
2.0
4.3
3.0
1.0
2.6
4.0
3.0
2.0
2.0
1.0
2.0
1.0
3.0
1.0
3.0
1.7
3.0
3.0
2.3
3.5
4.0
3.0
3.0
4.0
3.0
2.0
4.0
3.0
3.0
5.0
90
Preslia 82: 81–96, 2010
9
8
Non-invading
Naturalized
1C-value (pg DNA)
7
6
5
4
3
2
Geraniaceae (1/1)
Poaceae (401/4)
Ranunculaceae (1 51/1)
Nyctaginaceae (5/1)
Primulaceae (3/1)
Asteraceae (33 2/22)
Apiaceae (44/5)
Papaveraceae (30/1)
Apocynaceae (8/1)
Portulacaceae (6/1)
Dipsacaceae (2 /1)
Malvacea e (55/1)
Solanaceae (1 66/1)
Caryophyllaceae (29/2)
Cannabaceae (3 /1 )
Phytolaccaceae (6/1)
Balsaminaceae (1/2)
Fabaceae (531/5)
Polemoniaceae (1/1)
Plantaginaceae (33/3)
Lamiaceae (20 /1 )
Onagraceae (21 /4 )
Amaranthaceae (37/7)
Juncaceae (20/1)
Convolvulaceae (26/1)
Cucurbitaceae (2 9/1)
Oxa lidaceae (53/3)
Polygonaceae (12 /4 )
Brassicaceae (30/9)
Rosaceae (77/2)
0
Crassulaceae (15/3 )
1
Family
Fig. 3. – Comparison of median genome sizes (1C-values) of naturalized aliens with those of their non-invading
confamilials in 31 plant families. Genome sizes for non-invading species were taken from the Plant DNA C-values database (Bennet & Leitch 2005), those known to be naturalized or invasive in any part of the world were
excluded. Plant families are sorted according to the genome size of non-invading species. Numbers of species
(non-invading/naturalized) are shown in parentheses.
Discussion
Genome size variation
We determined nuclear DNA amounts in a representative set of naturalized plant species in
the flora of the Czech Republic and compared their values with genome sizes of noninvading species taken from the Plant DNA C-values database (Bennett & Leitch 2005).
Out of 93 naturalized species included, 66 (= 71%) were analyzed for the first time. In
addition, the first record was obtained for the family Phrymaceae, which had a very small
genome (Mimulus guttatus; 1C = 0.37 pg).
A comparison of genome size values for the same species as determined in our study
with those extracted from the database (Bennett & Leitch 2005) revealed some discrepancies. Disregarding variation caused by potential differences in ploidy level, the average
absolute difference in C-values was 28%. While about one third of the species (nine out of
26) showed differences below 10% (which is within the acceptable between-laboratory
limit as suggested by Doležel et al. 1998), four species differed more than 1.5-fold
(Amaranthus retroflexus, Solidago canadensis, Galinsoga parviflora and Antirrhinum
majus). It should, however, be noted that the difference largely depended on the methodology used. The best congruency between our data and the database values was observed for
measurements performed using propidium iodide flow cytometry (absolute difference <
Kubešová et al.: Naturalized plants have small genomes
91
10%, n = 4), which is generally recommended as the most reliable technique for genome
size estimation in plants (Greilhuber et al. 2007, Temsch et al. 2010). Species analyzed
either by Feulgen densitometry (which is much more sensitive to working conditions;
Greilhuber 2005) or flow cytometry with base-selective fluorochromes (Doležel et al.
1992) showed higher differences (30%, n = 21 and 54%, n = 1, respectively). Whereas
small differences in determined genome sizes can be explained by minor variation in
adopted protocols between laboratories (use of different buffers, different internal reference standards, etc.), it is possible that more serious methodological flaws were involved
in other cases and such data should be treated with caution.
Very small and small genomes (in the sense of the classification of genome sizes
defined by Leitch et al. 1998) clearly prevailed in our data set, accounting for 53 and 39%
of the species total, respectively. This is a dramatically different frequency of individual
genome size categories as compared to non-invading species (Table 2). For example,
while intermediate genomes (1C = 3.51–14.0 pg) are as common as the very small ones
(1C ≤ 1.4 pg) in non-invading plants, their ratio drops down to only one seventh of the frequency of very small genomes in naturalized aliens. Significantly smaller genomes in naturalized plants as compared to their phylogenetically related non-invading counterparts
were also confirmed at both taxonomic levels tested, i.e., the rank of genus and family. The
same pattern of genome size variation as in naturalized plants (i.e. predominance of species with low nuclear DNA amounts and the lack of DNA-obese species) was observed,
for instance, in weedy plants (Bennett et al. 1998) or in endemics on oceanic islands (Suda
et al. 2005). Selection for rapid development, fast growth, and production of many light
and easily dispersible seeds are plausible evolutionary forces that constrain the genome
size in these plant groups.
The presence of species with different life histories allowed us to test the potential association between genome size and life history (Bennett 1972). Although basic descriptive
statistics for 36 polycarpic perennial plants (mean and median 1C-values 2.44 pg and 1.73
pg, respectively) somehow differed from corresponding values for both 36 annuals (mean
= 1.58 pg, median = 1.10 pg) and 21 monocarpic species (mean = 1.65 pg, median = 1.15
pg), the differences were not statistically significant.
Relationship between genome size and invasion success
By using the data set analyzed in this study, we were unable to detect the effect of any species traits examined on the genome size. However, it should be noted that the low test
power of the model does not allow us to conclude that such effects do not exist. The analysis was carried out with individual species as random independent data points. This can
inflate degrees of freedom, because the species can be mutually dependent due to their
phylogenetic relatedness (e.g. Harvey & Pagel 1991). However, removing phylogenetic
effects from the nonsignificant general linear model would require methods based on
eigenvector filtering (Diniz-Filho et al. 1998) and repeating the analysis after this correction could thus only further decrease the statistical significance of the results. That genome
size is associated with invasion success is clearly demonstrated by the comparison of naturalized aliens in the Czech flora with the reference global set of non-invading congeners.
In this analysis the effect of phylogenetic relatedness, which was shown to bias the effect
of traits on species’ invasion success (e.g. Crawley et al. 1996, Pyšek 1997, Goodwin et al.
92
Preslia 82: 81–96, 2010
1999, Grotkopp et al. 2004, Hamilton et al. 2005, Lloret et al. 2005, Cadotte et al. 2006)
was suppressed by the congeneric comparison. This is a convenient approach to studying
the role of species traits in plant invasions (Pyšek & Richardson 2007, Perglová et al.
2009).
Our results therefore provide robust evidence, based on a large number of species
across a wide range of plant families, that alien species that successfully naturalize have
smaller genomes than those that do not reach the stage of naturalization. It should be, however, noted that sample size for some families was rather limited (e.g. only one naturalized
and/or non-invading species was available for 18 out of 31 families used for comparison),
which may limit the generality of our conclusions and calls for further comparative studies. The association of small genome size with invasiveness was previously suggested in
a number of studies (Rejmánek 1996, 2000, Grotkopp et al. 2002, Rejmánek et al. 2005,
Garcia et al. 2008). Small genome size seems to be a result of selection for short minimum
generation time. It is also associated with small seed size, high leaf area ratio and high relative growth rate of seedlings (Grotkopp et al. 2002), and as such may be an ultimate determinant of plant species invasiveness in disturbed habitats (Rejmánek 1996, Bennett et al.
1998, Grotkopp et al. 1998, Rejmánek 2000).
However, studies that addressed the role of genome size in plant species’ invasiveness
usually compared invasive and non-invasive species and did not distinguish between species at different stages of the invasion process. In our data there was no difference in the
genome size of invasive species compared to naturalized but non-invasive species. This
indicates that the small genome size may provide alien plants with an advantage already at
the stage of naturalization and need not necessarily play a role during the follow-up step,
transition from naturalized to invasive species. It also points to the importance of distinguishing the stages of invasion in such studies since the determinants of invasion success
may differ between stages (Williamson 2006, Pyšek et al. 2008, 2009a, b).
See http://www.preslia.cz for Electronic Appendix 1.
Acknowledgements
The study was funded by grants no. 206/05/0323, 206/09/0563 and 206/08/H049 from the Czech Science Foundation, long-term research plans no. AV0Z60050516 (from the Academy of Sciences of the Czech Republic) and
no. MSM0021620828, project LC06073 (both from the Ministry of Education, Youth and Sports of the Czech
Republic), and no. 261 211 (Grant Agency of Charles University). We thank Laura Meyerson and Johann
Greilhuber for helpful comments on the manuscript, Ewald Weber for providing us with an updated version of his
database of alien plants of the world, Milan Chytrý for consultation on habitat moisture classification, David
Richardson for improving our English, Vendula Havlíčková for technical assistance and all colleagues who provided us with locality details and/or helped with seed collection.
Souhrn
Velikost genomu bývá považována za vlastnost ovlivňující invazivnost rostlinných druhů. V článku je tato souvislost testována na souboru 93 nepůvodních naturalizovaných druhů české flóry ze 32 čeledí, u nichž byl změřen
obsah jaderné DNA metodou průtokové cytometrie. Hodnoty získané pro naturalizované druhy byly srovnány
s hodnotami udávanými v databázi velikosti genomu rostlin pro druhy ze stejných rodů a čeledí, o nichž není známo, že by byly někde ve světě invazní. Ukázalo se, že druhy naturalizované v České republice mají statisticky průkazně menší genom než neinvazní druhy ze stejných rodů. Tento trend potvrdilo i srovnání naturalizovaných druhů s druhy ze stejných čeledí; zde byl zjištěn menší genom u 19 z 31 analyzovaných čeledí. Nepůvodní naturalizo-
Kubešová et al.: Naturalized plants have small genomes
93
vané druhy oproti druhům neinvazním navíc vykazovaly i zcela odlišné zastoupení jednotlivých kategorií velikosti genomu, nápadná je zejména výrazná převaha velmi malých genomů a velice nízký podíl druhů s velkými
genomy. Tyto výsledky jsou prvním kvantitativním potvrzením založeném na velkém počtu druhů, že malé genomy přispívají k invazivnosti rostlinných druhů. Přitom invazní druhy v analyzovaném souboru se nelišily od druhů naturalizovaných, leč neinvazních. To ukazuje, že působení malého genomu jakožto vlastnosti výhodné pro
invazi je spíše spojeno se stádiem naturalizace, zatímco při přechodu do stádia vlastní invazi již tak významné být
nemusí.
References
Bennett M. D. (1972): Nuclear DNA content and minimum generation time in herbaceous plants. – Proc. R. Soc.
London B 181: 109–135.
Bennett M. D. (1987): Variation in genomic form in plants and its ecological implications. – New Phytol. 106
(Suppl.): 177–200.
Bennett M. D. & Leitch I. J. (2005): Plant DNA C-values database (release 4.0, Oct. 2005). – URL:
[http://www.kew.org/cvalues/].
Bennett M. D., Leitch I. J. & Hanson L. (1998): DNA amounts in two samples of angiosperm weeds. – Ann. Bot.
82: 121–134.
Binimelis R., Born W., Monterroso I. & Rodríguez-Labajos B. (2007): Socio-economic impacts and assessment
of biological invasions. – In: Nentwig N. (ed.), Biological invasions, p. 331–347, Springer, Berlin.
Blackburn T. M., Lockwood J. L. & Cassey P. (2009): Avian invaders: the ecology and evolution of exotic birds. –
Oxford University Press, Oxford.
Cadotte M. W., Murray B. R. & Lovett-Doust J. (2006): Evolutionary and ecological influences of plant invader
success in the flora of Ontario. – Ecoscience 13: 388–395.
Chytrý M., Maskell L. C., Pino J., Pyšek P., Vilŕ M., Font X. & Smart S. M. (2008): Habitat invasions by alien
plants: a quantitative comparison among Mediterranean, subcontinental and oceanic regions of Europe. – J.
Appl. Ecol. 45: 448–458.
Chytrý M., Pyšek P., Tichý L., Knollová I. & Danihelka J. (2005): Invasions by alien plants in the Czech Republic:
a quantitative assessment across habitats. – Preslia 77: 339–354.
Chytrý M., Wild J., Pyšek P., Tichý L., Danihelka J. & Knollová I. (2009): Maps of the level of invasion of the
Czech Republic by alien plants. – Preslia 81: 187–207.
Crall A. W., Meyerson L. A., Stohlgren T. J., Jarnevich C. S., Newman G. J. & Graham J. (2006): Show me the
numbers: what data currently exist for non-native species in the USA? – Front. Ecol. Environ. 4: 414–418.
Crawley M. J. (1993): GLIM for Ecologists. – Blackwell, Oxford.
Crawley M. J. (2002): Statistical computing: an introduction to data analysis using S-Plus. – Wiley, Chichester.
Crawley M. J., Harvey P. H. & Purvis A. (1996): Comparative ecology of the native and alien floras of the British
Isles. – Biol. Trans. R. Soc. B 351: 1251–1259.
DAISIE (2009): Handbook of alien species in Europe. – Springer, Berlin.
Davis M. A. (2009): Invasion biology. – Oxford University Press, Oxford.
Davis M. A., Grime J. P. & Thompson K. (2000): Fluctuating resources in plant communities: a general theory of
invasibility. – J. Ecol. 88: 528–534.
Diniz-Filho J. A. F., De Santana C. E. R. & Bini L. M. (1998): An eigenvector method for estimating phylogenetic
inertia. – Evolution 52: 1247–1262.
Doležel J., Greilhuber J., Lucretti S., Meister A., Lysák M. A., Nardi L. & Obermayer R. (1998): Plant genome
size estimation by flow cytometry: inter-laboratory comparison. – Ann. Bot. 82 (Suppl. A): 17–26.
Doležel J., Greilhuber J. & Suda J. (2007): Estimation of nuclear DNA content in plants using flow cytometry. –
Nature Protoc. 2: 2233-2244.
Doležel J., Sgorbati S. & Lucretti S. (1992): Comparison of three DNA fluorochromes for flow cytometric estimation of nuclear DNA content in plants. – Physiol. Plant. 85: 625–631.
Ekrt T., Trávníček P., Jarolímová V., Vít P. & Urfus T. (2009): Genome size and morphology of the Dryopteris
affinis group in Central Europe. – Preslia 81: 261–280.
Ellenberg H., Weber H. E., Düll R., Wirth W., Werner W. & Paulißen D. (1992): Zeigerwerte von Pflanzen in
Mitteleuropa. Ed. 2. – Scripta Geobotanica 18: 1–258.
Essl F., Dullinger D. & Kleinbauer I. (2009): Changes in the spatio-temporal patterns and habitat preferences of
Ambrosia artemisiifolia during the invasion of Austria. – Preslia 81: 119–133.
Gaertner M., Breeyen A. D., Hui C. & Richardson D. M. (2009): Impacts of alien plant invasions on species richness in Mediterranean-type ecosystems: a meta-analysis. – Progr. Phys. Geogr. 33: 319–338.
94
Preslia 82: 81–96, 2010
Garcia S., Canela M. A., Garnatje T., McArthur E. D., Pellicer J., Sanderson S. C. & Vallés J. (2008): Evolutionary and ecological implications of genome size in the North American endemic sagebrushes and allies (Artemisia, Asteraceae). – Biol. J. Linn. Soc. 94: 631–649.
Goldblatt P. & Johnson D. E. (eds) (1979 onwards): Index to plant chromosome numbers. – Missouri Botanical
Garden, St. Louis, URL: [http://mobot.mobot.org/W3T/Search/ipcn.html].
Goodwin B. J., McAllister A. J. & Fahrig L. (1999): Predicting invasiveness of plant species based on biological
information. – Conserv. Biol. 13: 422–426.
Gregory T. R. (2005): The C-value enigma in plants and animals: a review of parallels and an appeal for partnership. – Ann. Bot. 95: 133-146.
Greilhuber J. (2005): Intraspecific variation in genome size in angiosperms: identifying its existence. – Ann. Bot.
95: 91–98.
Greilhuber J., Doležel J., Lysák M. & Bennett M. D. (2005): The origin, evolution and proposed stabilization of
the terms ‘genome size’ and ‘C-value’ to describe nuclear DNA contents. – Ann. Bot. 95: 255–260.
Greilhuber J., Temsch E. M. & Loureiro J. C. M. (2007): Nuclear DNA content measurement. – In: Doležel J.,
Greilhuber J. & Suda J. (eds), Flow cytometry with plant cells, p. 67–101, Wiley-VCH, Weinheim.
Grotkopp E., Rejmánek M. & Rost T. L. (2002): Toward a causal explanation of plant invasiveness: seedling
growth and life-history strategies of 29 pine (Pinus) species. – Am. Nat. 159: 396–419.
Grottkop E., Rejmánek M., Sanderson M. J. & Rost T. L. (2004): Evolution of genome size in pines (Pinus) and
its life-history correlates: supertree analyses. – Evolution 58: 1705–1729.
Grotkopp E., Stoltenberg R., Rejmánek M. & Rost T. L. (1998): The effect of genome size on invasiveness. – Am.
J. Bot. 85 (Suppl.): 34.
Hamilton M. A., Murray B. R., Cadotte M. W., Hose G. C., Baker A. C., Harris C. J. & Licari D. (2005): Life-history correlates of plant invasiveness at regional and continental scales. – Ecol. Lett. 8: 1066–1074.
Harvey P. H. & Pagel M. D. (1991): The comparative method in evolutionary biology. – Oxford University Press,
Oxford.
Hejda M., Pyšek P. & Jarošík V. (2009a): Impact of invasive plants on the species richness, diversity and composition of invaded communities. – J. Ecol. 97: 393–403.
Hejda M., Pyšek P., Pergl J., Sádlo J., Chytrý M. & Jarošík V. (2009b): Invasion success of alien plants: do habitats affinities in the native distribution range matter? – Glob. Ecol. Biogeogr. 18: 372–382.
Hejný S. & Slavík B. (eds) (1988–1992): Květena ČR [Flora of the Czech Republic]. Vol. 1 (1988), 2 (1990), 3
(1992). – Academia, Praha.
Hulme P. E., Bacher S., Kenis M., Klotz S., Kühn I., Minchin D., Nentwig W., Olenin S., Panov V., Pergl J., Pyšek
P., Roques A., Sol D., Solarz W. & Vilà M. (2008): Grasping at the routes of biological invasions: a framework
for integrating pathways into policy. – J. Appl. Ecol. 45: 403–414.
Hulme P. E., Nentwig W., Pyšek P. & Vilà M. (2009a): Common market, shared problems: time for a coordinated
response to biological invasions in Europe? – Neobiota 8: 3–19.
Hulme P., Pyšek P., Nentwig W. & Vilà M. (2009b): Will threat of biological invasions unite the European
Union? – Science 324: 40–41.
Keller R., Lodge D. M. & Finnoff D. (2007): Risk assessment for invasive species produces net bioeconomic benefits. – Proc. Natl Acad. Sci. USA 104: 203–207.
Kettunen M., Genovesi P., Gollasch S., Pagad S., Starfinger U., ten Brink P. & Shine C. (2009): Technical support
to EU strategy on invasive species (IAS): assessment of the impacts of IAS in Europe and the EU (final module report for the European Commission). – Institute for European Environmental Policy, Brussels.
Knight C. A., Molinari N. A. & Petrov D. A. (2005): The large genome constraint hypothesis: evolution, ecology
and phenotype. – Ann. Bot. 95: 177–190.
Kron P., Suda J. & Husband B. C. (2007): Applications of flow cytometry to evolutionary and population biology. – Annu. Rev. Ecol. Evol. Syst. 38: 847–876.
Lambdon P. W., Pyšek P., Basnou C., Hejda M., Arianoutsou M., Essl F., Jarošík V., Pergl J., Winter M.,
Anastasiu P., Andriopoulos P., Bazos I., Brundu G., Celesti-Grapow L., Chassot P., Delipetrou P., Josefsson
M., Kark S., Klotz S., Kokkoris Y., Kühn I., Marchante H., Perglová I., Pino J., Vilà M., Zikos A., Roy D. &
Hulme P. E. (2008): Alien flora of Europe: species diversity, temporal trends, geographical patterns and
research needs. – Preslia 80: 101–149.
Lawrence M. E. (1985): Senecio L. (Asteraceae) in Australia: nuclear DNA amounts. – Aust. J. Bot. 33: 221–232.
Leitch, I. J. & Bennett M. D. (2007). Genome size and its uses: the impact of flow cytometry. – In: Doležel J.,
Greilhuber J. & Suda J. (eds), Flow cytometry with plant cells, p. 153–176, Wiley-VCH, Weinheim.
Leitch I. J., Chase M. W. & Bennett M. D. (1998): Phylogenetic analysis of DNA C-values provides evidence for
a small ancestral genome size in flowering plants. – Ann. Bot. 82 (Suppl. A): 85–94.
Kubešová et al.: Naturalized plants have small genomes
95
Levine J. M., Vilà M., D’Antonio C. M., Dukes J. S., Grigulis K. & Lavorel S. (2003): Mechanisms underlying
the impacts of exotic plant invasions. – Proc. R. Soc. London B 270: 775–781.
Lloret F., Médail F., Brundu G., Camarda I., Moragues E., Rita J., Lambdon P. & Hulme P. E. (2005): Species
attributes and invasion success by alien plants on Mediterranean islands. – J. Ecol. 93: 512–520.
Loureiro J., Trávníček P., Rauchová J., Urfus T., Vít P., Štech M., Castro S. & Suda J. (2010): The use of flow
cytometry in the biosystematics, ecology and population biology of homoploid plants. – Preslia 82: 3–21.
Marhold K., Mártonfi P., Mereďa jun. P., Mráz P., Hodálová I., Kolník M., Kučera J., Lihová J., Mrázová V., Perný
M. & Valko I. (2007): Karyologická databáza papraďorastov a semenných rastlín Slovenska [Karyological
database of the ferns and flowering plants of Slovakia], ver. 1. – URL: [http://www.chromosomes.sav.sk].
McGeoch M. A., Butchart S. H. M., Spear D., Marais E., Kleynhans E. J., Symes A., Chanson J. & Hoffmann M.
(2010): Global indicators of biological invasion: species numbers, biodiversity impact and policy responses. –
Diversity Distrib. 16: 95–108.
Meyerson L. A. & Mooney H. A. (2007): Invasive alien species in an era of globalization. – Front. Ecol. Environ.
5: 199–208.
Mukherjee S. & Sharma A. K. (1990): Mitotic cycle duration and its relationship with nuclear DNA content,
chromosome number and size and rate of growth in species of Acacia growing under stress. – Ind. J. Exp.
Biol. 28: 508–510.
Nentwig W., Kühnel E. & Bacher S. (2010): A generic impact-scoring system applied to alien mammals in
Europe. – Cons. Biol. 204: 302–311.
Otto F. (1990): DAPI staining of fixed cells for high-resolution flow cytometry of nuclear DNA. – In: Crissman H.
A. & Darzynkiewicz Z. (eds), Methods in cell biology 33: 105–110, Academic Press, New York.
Perglová I., Pergl J., Skálová H., Moravcová L., Jarošík V. & Pyšek P. (2009): Differences in germination and
seedling establishment of alien and native Impatiens species. – Preslia 81: 357–375.
Pyšek P. (1997): Clonality and plant invasions: can a trait make a difference? – In: de Kroon H. & van
Groenendael J. (eds), The ecology and evolution of clonal plants, p. 405–427, Backhuys Publishers, Leiden.
Pyšek P., Jarošík V. , Pergl J., Randall R., Chytrý M., Kühn I., Tichý L., Danihelka J., Chrtek jun. J. & Sádlo J.
(2009a): The global invasion success of Central European plants is related to distribution characteristics in
their native range and species traits. – Diversity Distrib. 15: 891–903.
Pyšek P., Křivánek M. & Jarošík V. (2009b): Planting intensity, residence time, and species traits determine invasion success of alien woody species. – Ecology 90: 2734–2744.
Pyšek P. & Richardson D. M. (2007): Traits associated with invasiveness in alien plants: where do we stand? – In:
Nentwig W. (ed.), Biological invasions, p. 97–125, Springer-Verlag, Berlin & Heidelberg.
Pyšek P., Richardson D. M. & Jarošík V. (2006): Who cites who in the invasion zoo: insights from an analysis of
the most highly cited papers in invasion ecology. – Preslia 78: 437–468.
Pyšek P., Richardson D. M., Pergl J., Jarošík V., Sixtová Z. & Weber E. (2008): Geographical and taxonomic
biases in invasion ecology. – Trends Ecol. Evol. 23: 237–244.
Pyšek P., Richardson D. M., Rejmánek M., Webster G., Williamson M. & Kirschner J. (2004): Alien plants in
checklists and floras: towards better communication between taxonomists and ecologists. – Taxon 53:
131–143.
Pyšek P., Sádlo J. & Mandák B. (2002): Catalogue of alien plants of the Czech Republic. – Preslia 74: 97–186.
Rejmánek M. (1996): A theory of seed plant invasiveness: the first sketch. – Biol. Cons. 78: 171–181.
Rejmánek M. (2000): Invasive plants: approaches and predictions. – Austral Ecol. 25: 497–506.
Rejmánek M., Richardson D. M. & Pyšek P. (2005): Plant invasions and invasibility of plant communities. – In:
Van der Maarel E. (ed.), Vegetation ecology, p. 332–355, Blackwell Science, Oxford.
Ricciardi A. & MacIsaac H. J. (2008): The book that began invasion ecology. – Nature 452: 34.
Richardson D. M., Holmes P. M., Esler K. J., Galatowitsch S. M., Stromberg J. C., Kirkman S. P., Pyšek P. &
Hobbs R. J. (2007): Riparian vegetation: degradation, alien plant invasions, and restoration prospects. –
Diversity Distrib. 13: 126–139.
Richardson D. M. & Pyšek P. (2008): Fifty years of invasion ecology: the legacy of Charles Elton. – Diversity
Distrib. 14: 161–168.
Richardson D. M., Pyšek P., Rejmánek M., Barbour M. G., Panetta F. D. & West C. J. (2000): Naturalization and
invasion of alien plants: concepts and definitions. – Diversity Distrib. 6: 93–107.
Simberloff D. (2009): We can eliminate invasions or live with them: successful management projects. – Biol. Inv.
11: 149–157.
Slavík B. (ed.) (1995–2000): Květena ČR [Flora of the Czech Republic]. Vol. 4 (1995), 5 (1997), 6 (2000). – Academia, Praha.
Slavík B. & Štěpánková J. (eds) (2004): Květena ČR 8 [Flora of the Czech Republic. Vol. 8]. – Academia, Praha.
96
Preslia 82: 81–96, 2010
Sokal R. R. & Rohlf F. J. (1995): Biometry. Ed. 3. – Freeman, New York.
Štajerová K., Šmilauerová M. & Šmilauer P. (2009): Arbuscular mycorrhizal symbiosis of herbaceous invasive
neophytes in the Czech Republic. – Preslia 81: 341–355.
Steidel R. J. & Thomas L. (2001): Power analysis and experimental design. – In: Scheiner S. M. & Gurevitch J.
(eds), Design and analysis of ecological experiments, Ed. 2., p. 14–36, Oxford University Press, Oxford.
Stevens P. F. (2001 onwards): Angiosperm Phylogeny Website. Version 9, June 2008. – URL:
[http://www.mobot.org/MOBOT/Research/APweb/welcome.html].
Suda J., Kyncl T. & Jarolímová V. (2005): Nuclear DNA amounts in Macaronesian angiosperms: forty percent of
Canarian endemic flora completed. – Plant Syst. Evol. 252: 215–238.
Temsch E. M., Greilhuber J. & Krisai R. (2010): Genome size in liverworts. – Preslia 82: 63–80.
Vidic T., Greilhuber J., Vilhar B. & Dermastia M. (2009): Selective significance of genome size in a plant community with heavy metal pollution. – Ecol. Appl. 19: 1515–1521.
Vilà M., Basnou C., Pyšek P., Josefsson M., Genovesi P., Gollasch S., Nentwig W., Olenin S., Roques A., Roy D.,
Hulme P. E. & DAISIE partners (2010): How well do we understand the impacts of alien species on ecological
services? A pan-European cross-taxa assessment. – Front. Ecol. Environ. 8: 135–144.
Wakamiya I., Newton R. J., Johnston J. S. & Price H. J. (1993): Genome size and environmental factors in the
genus Pinus. – Am. J. Bot. 80:1235–1241.
Weber E. (2003): Invasive plant species of the world: a reference guide to environmental weeds. – CAB International Publishing, Wallingford.
Williamson M. (2006): Explaining and predicting the success of invading species at different stages of invasion. –
Biol. Inv. 8: 1561–1568.
Received 12 March 2010
Revision received 28 March 2010
Accepted 30 March 2010